Process for producing a synthetic paper

ABSTRACT

A synthetic paper comprising an olefinic resin is produced by stretching an unstretched sheet of an olefinic resin such as polyethylene under the temperature conditions (1) or (2) below: 1. AT A TEMPERATURE LOWER THAN THE MELTING TEMPERATURE OF SAID RESIN, THE TEMPERATURE OF THE INNER LAYER OF THE SHEET BEING DIFFERENT FROM THAT OF BOTH SURFACE LAYERS BY AT LEAST 10*C., and 2. AT A TEMPERATURE SUCH THAT EITHER ONE OF THE SURFACE LAYERS AND THE INNER LAYER IS MAINTAINED AT A TEMPERATURE LOWER THAN THE MELTING TEMPERATURE OF SAID RESIN, AND THE OTHER IS MAINTAINED AT A TEMPERATURE NOT LOWER THAN THE MELTING TEMPERATURE OF SAID RESIN AND HIGHER THAN THE MELTING TEMPERATURE BY 40*C. or less. The synthetic paper is light in weight and has high strength in addition to other desirable properties and finds utility as packaging and printing.

United States Patent 1191 Yamamoto et al.

1 PROCESS FOR PRODUCING A SYNTHETIC PAPER [75] Inventors: Sadao Yamamoto, Kyoto; Seiichirou Honda, lbaraki; Akira Nishio, Takatsuki, all of Japan [73] Assignee: Sekisui Kagaku Kogyo Kabushiki Kaisha, Osaka, Japan 22 Filed: Dec. 24, 1970 211 App]. No; 101,436

[30] Foreign Application Priority Data Dec. 26, 1969 Japan 44/539 Dec. 26, 1969 Japan 44/540 Dec. 29, 1969 Japan 44/219 Jan. 12, 1970 Japan 45/3674 .Ian. 12, 1970 Japan 45/3675 Jan. 12, 1970 Japan 45/3676 Jan. 16, 1970 Japan 45/4656 Jan. 16, 1970 Japan 45/4657 [52] U.S. CI 264/230, 161/164, 161/165,

264/289, 264/342 R, 264/345, 264/D1G. 13, 264/D1G. 71, 264/D1G. 73

[51] Int. Cl. B29c 17/02, B29d 7/22, 829d 7/24 [58] Field of Search 264/D1G. 13, 210 R, 264/284, 288, 289, 345, 342 R, 230, DIG. 71,

DIG. 73; 260/41 A, 41 B, 889,896, 897; 161/164,165, 402, 410

[56} References Cited UNITED STATES PATENTS 3,234,313 2/1966 Miller et a1. 264/230 [451 Sept. 11, 1973 Primary ExaminerPhilip E. Anderson Attorney'-Wenderoth, Lind & Ponack [57] ABSTRACT A synthetic paper comprising an oleflnic resin is produced by stretching an unstretched sheet of an olefinic resin such as polyethylene under the temperature conditions (1) or (2) below: A

1. at a temperature lower than the melting temperature of said resin, the temperature of the inner layer of the sheet being different from that of both surface layers by at least 10C., and 2. at a temperature such that either one of the surface layers and the inner layer is maintained at a temperature lower than the melting temperature of said resin, and the other is maintained at a temperature not lower than the melting temperature of said resin and higher than the melting temperature by 40C. or less.

The synthetic paper is light in weight and has high 6 Claims, No Drawings Gregorian et al 264/230 X PROCESS FOR PRODUCING A SYNTHETIC PAPER This invention relates to a process for producing a synthetic paper, and more specifically, to a process for producing a synthetic paper comprising an olefinic resin, which is light in weight and has high strength.

A process for producing a synthetic paper by stretching an unstretched sheet composed of an olefinic resin and a filler has heretofore been known. But this prior method cannot give a synthetic paper in which voids are uniformly distributed along its entire sectional area. A sheet having voids of large size distributed uniformly has a rough surface and good graphic properties with a writing instrument such as pen and pencils, and is moreover light in weight, but has the defect of considerably inferior strength. Conversely, a sheet having uniformly distributed voids of smaller size has satisfactory strength, but cannot be free from the defect of the heavy weight of synthetic paper.

With a view to removing these defects, we have attempted to produce a sheet whose upper and lower surfaces have voids of different sizes by passing an unstretched sheet of an olefinic resin between rolls having a difference in temperature by at least C. In the resulting sheet, the size of voids on one surface is larger than that of the voids on the other. Hence, this sheet is satisfactory to some extent in its light weight and retention of strength. However, the'physical properties of one surface differ from those of the other, and the sheet is often broken during printing owing to tension exerted on the sheet or blur occurs during printing. Thus, the sheet has only limited applications.

Accordingly, an object of the present invention is to provide a synthetic paper comprising an olefinic resin which has eliminated the aforementioned defects.

The synthetic paper produced according to the invention has a symmetrical void size distribution with respect to the horizontal center line of any section of the sheet when viewed macroscopically, and in the sectional structure of the stretched sheet of the olefinic resin, the void size of the inner layer differs from that of both surface layers. The synthetic paper of the. invention is light in weight, and has high physical strengths such as tensile strength, tear strength or bending strength. Furthermore, it does not break under strain stress, and is good in printability with an aqueous or oily ink, stamps or typewriters, and graphic properties with a writing instrument such as pencils or pens.

According to the invention, there is provided a process for producing a synthetic paper which comprises stretching an unstretched sheet of an olefinic resin under temperature conditions (1) or (2) l. at a temperature lower than the melting temperature of said resin, the temperature of the inner layer of the sheet being different from thatof both surface layers by at least 10C., and

2. at a temperature such that either one of the surface layers and the inner layer is at a temperature lower than the melting temperature of said resin, and the other is at a temperature not lower than the melting temperature of said resin and higher than the melting temperature by 40C. or less.

The term melting temperature" of the olefinic resin, as used in the specification and the appended claims, means the temperature above which crystals are no longer present (where the olefinic resin is crystalline); and the temperature above which the resin rapidly tends to flow (where the olefinic resin is non-crystalline or has extremely small crystallinity).

The olefinic resin to be used in the invention includes, homopolymers or copolymers of a-olefins, especially C -C a-olefins, and their blends. It is desirable that the olefinic resin should have a melt index of not over 10, preferably from 0.01 to 5.

Specific examples of the homopolymers of C -C., a-olefins include high pressure polyethylene, medium pressure polyethylene, low pressure polyethylene, polypropylene and polybutene-l, and said homopolymers whose optional positions have been replaced by other atoms or atomic groups, such as chlorinated polyethylene or chlorinated polypropylene.

Examples of the copolymers of C,,-C a-olefins are those of at least 50 percent of the a-olefins with a monomer copolymerizable therewith, for instance, ethylene/vinyl acetate copolymer, ethylene/vinyl chloride copolymer, ethylene/styrene copolymer, ethylene/ethyl acrylate copolymer, ethylene/propylene copolymer, ethylene/ propylene/vinyl chloride copoly mer, propylene/styrene copolymer, propylene/ethyl acrylate copolymer, and propylene/vinyl acetate copoly mer.

The olefinic resin to be used in the present invention can be blended with a resin having poor compatibility with the olefinic resin in an amount of up to 100 parts by weight, preferably from 5 to parts by weight, per parts by weight of said olefinic resin.

By the term resin having poor compatability with the olefinic resin is meant a resin which is not completely compatible with the olefinic resin but does not undergo substantial phase separation when blended with the olefinic resin in the process of producing an unstretched sheet. Assuch resin, there can be cited styrene resinssuch as a homopolymer of styrene, a homopolymer of a styrene derivative such as a-methyl styrene, styrene/a-methylstyrene copolymer, and copolymers of styrene or styrene derivatives with other copolymerizable monomers, for example, styrene/methylmethacrylate copolymer, styrene/acrylonitrile copolymer, styrene/butadiene/acrylonitrile copolymer, methylmethacrylate/butadiene/styrene copolymer or wmethylstyrene/methylmethyacrylate copolymerypolyamide resins produced by the condensation of aminocarboxylic acids and the condensation between dibasic acids and diamines, such as nylon 66, nylon 6, nylon 610 and nylon 11; polyacetal resins such as a polymer of formaldehyde, or thermoplastic copolymers of formaldehyde with other copolymerizable monomers, for example, commercially available Delrin (trademark, Du Pont), Celan'ese (tradename, Cellanese Corporation), or Duracon (tradename, Polyplastics Corporation); polyacrylate resins such as methyl methacrylate resin, methyl methacrylate/styrene copolymer, methyl methacrylate/a-methylstyrene copolymer, and copolymers of methyl methacrylate with other copolymerizable monomers; vinyl chloride resins such as polyvinyl chloride, vinyl chloride/vinyl acetate copolymer, vinyl chloride/ethylene copolymer, vinyl' chloride/vinyliderie, and copolymers of vinyl chloride with other copolymerizable monomers; vinyl acetate resins such as vinyl acetate, vinyl acetate/vinyl chloride copolymer, vinyl acetate/ethylene copolymer, and copolymers of vinyl acetate with other copolymerizable monomers; phenoxy resins such as thermoplastic epoxy resins obtained by cocondensation of bisphenol A and epichlorohydrin; and rubbery high-molecularweight substances such as polyisoprene, polyisobutylene, polybutadiene, polypropylene oxide, rubber ethylene/propylene copolymer, butyl rubber, styrene/- butadiene rubber, acrylonitrile rubber, chloroprene rubber, various acrylic rubbers, and natural rubbers.

Finely divided powders of an inorganic filler may be incorporated in the olefinic resin used in the invention. Examples of such inorganic filler includediatomaceous earth, silica, talc, kaolin, zeolite, mica, asbestos, calcium carbonate, magnesium carbonate, calcium sulfate, clay, alumina, barium sulfate, zinc sulfate, lithopone, titanium oxide, and zinc flower, especially preferred being diatomaceous earth, silica, talc, kaolin, zeolite, mica, and asbestos. The amount of the inorganic filler to be incorporated is not more than 300 parts by weight, preferably from 20 to 200 parts by weight per 100 parts by weight of the olefinic resin.

According to the desired use of the synthetic paper of the present invention, heat stabilizers, plasticizers, antistatic agents, lubricants, ultraviolet ray absorbents, dyestuffs, pigments, and other additives may be incorporated in the homopolymers, copolymers or blends thereof of the olefmic resins that are used in the present invention.

According to the process of the present invention, the olefinic resin described is first fabricated into a sheet. The term sheet is meant to include foils, films and plates. The sheet formation can be accomplished by any conventional method, such as extrusion, injection, rolling, compression, or blowing. For example, the olefinic resin is thoroughly kneaded by such a machine as a Banbury mixer, mixing roll, or extrusion kneader, and the molten resin is subjected to calender rolling to form it into a sheet. Alternatively, the resin is put into an extruder with or without prior kneading in a Henschel mixer or super mixer, kneaded and melted in the extruder, and extruded into a sheet form.

The thickness of the unstretched sheet of the olefinic resin so obtained depends upon the subsequent stretching step, the applications of the synthetic sheet, etc. Usually, the preferred thickness is about 0.2 mm to 5.00 mm, particularly 0.3 mm to 3.0 mm.

The unstretched sheet so obtained is then stretched in accordance with the process of the present invention.

According to a first method of the invention, the unstretched sheet of the olefinic resin is stretched at a temperature lower than the melting temperature of said resin with a temperature difference of not less than C. provided between the inner layer and both surface layers of the sheet. This stretching leads to the produetion of a stretched sheet having a porous structure, in which the void size differs from the surface layers to the inner layer and macroscopically, the void size is symmetrical with respect to the center line of a section of the sheet. Depending upon the applications of the synthetic paper obtained by the invention, for instance, printing and writing, the void size ofthe surface layers can be made either smaller or larger-than that of the inner layer.

According to a first embodiment of-the invention, there is provided a process for stretching an unstretched sheet of the olefinic resin at a temperature lower than the melting temperature of the olefinic resin, the temperature of both surface layers being maintained at a point at least 10C. higher than that of the inner layer.

The product obtained according to the first embodiment exhibits good printability especially with printing ink as the void structure of the surface layers of the sheet is finer and denser than that of the inner layer. The small void size of the surface layers of the product of the invention serves to retain the physical strength of the sheet, and the larger void size of the inner layer contributes to the light weight of the sheet.

The stretched sheet obtained by the first embodiment of the process of the invention can be further stretchedv at a temperature below the melting temperature of the olefinic resin and at a temperature either higher or lower than the temperature of the surface layers employed in the initial stretching. This second stretching resultsin further improvement of the surface characteristics of the stretched sheet and reduction of the density of the sheet.

According to a second embodiment of the process of the invention, there is provided a process for stretching an unstretched sheet of the olefinic resin at a temperature lower than the melting temperature of the olefinic resin, the temperature of the inner layer of the sheet being maintained at a point at least 10C. higher than that of both surface layers.

The product obtained by the second embodiment is suitable for writing with pencils or pens as the void structure of the inner layer is finer and denser than that of both surface layers. The large void size of both surface layers of the product so obtained contributes to the light weight of the sheet, and the smaller void size of the inner layer serves to retain the physical strength of the sheet. I

The stretched sheet can further be stretched at a temperature below the melting temperature of the. olefinic resin and at a temperature either higher or lower than the temperature of the inner layer employed in the initial stretching. Thus, there can be obtained a product having more improved surface characteristics and lower density.

The temperature used for stretching an unstretched sheet can be determined by specifying the temperature of the surface layers after heating the unstretched sheet to the desired temperature of the inner layer. The temperature of the surface layers can be determined by various methods including a roll method in which the sheet is passed once or several times between hot or cold rolls maintained at a temperature differing from the inner layer temperature by at least 10C.; an air heating or cooling method in which air having a temperature differing from the inner layer temperature by at least l0C.; a heating oven or cooling oven method in which the sheet is passed through an oven maintained at a temperature differing from the inner layer temperature by at least 10C.; or a heating tank or cooling tank method in which the sheet is passed through a tank of oil or water having a temperature differing from the inner layer temperature by at least 10C.

It is preferred that the unstretched sheet be subjected to the temperature of the surface layers for the shortest possible time to avoid any influence of the surface layer temperature on the inner layer temperature.

The temperature used in the second stretching can be set by any of the above-mentioned methods for determining the temperature of the surface layers. In the second stretching, the temperature of the surface layers may be the same as or different from that of the inner layer.

The stretching may be carried out uniaxially or multiaxially at the same time or in the successive manner, by any conventional manner. The most common multiaxial stretching is a biaxial stretching in the longitudinal and transverse directions, and for this purpose, a tenter stretcher is conveniently used.

The stretch ratio may be such as to provide a void structure in the sheet, and differs according to the physical properties and uses, etc. of the product. Usually, in the case of the first stretching, the ratio in one direction is at least 1.5, preferably from 1.8 to 8, and in the ease of the second stretching, it is at least L2, preferably from 1.5 to 2.0.

According to a second method of the process of the invention, an unstretched sheet of the olefinic resin is stretched at a temperature such that either one of the surface layers and the inner layer is below the melting temperature of the olefinic resin and the other is not lower than the melting temperature of the resin and not higher than the melting temperature by more than 40C. 4

According to a first embodiment of the second method, there is provided a process for stretching an unstretched sheet of the olefinic resin at a temperature such that the surface layers are maintained at a temperature not lower than the meltingtemperature of the resin but higher than it by not more than 40C., and the inner layer is maintained at a temperature below the melting temperature of the resin.

The stretched sheet obtained by this embodiment is a tough and light sheet in which both surfaces are smooth and the inner layer has a porous structure. The sheets are suitable for printing with a printing ink which contains a solvent capable of dissolving the molten surface layer.

According to a second embodiment of the second process, there is provided a process for stretchingan unstretched sheet of the olefinic resin at a temperature such that the surface layers of the sheet is maintained at a temperature below the melting temperature of the resin and the inner layer is maintained at a temperature not lower than the melting temperature of the resin but higher than the melting temperature by not more than 40C. This process leads to the production of a stretched sheet having porous surface layers and a substantially voidless inner layer. Since such sheet has porous surface layers, it is not only superior in printability and graphic properties, but also is light in weight and tough because of a dense film layer present inside.

The stretched sheet obtained by the second method of the invention in which either the surface layers or the inner layer is substantially free from voids can, if desired, be stretched further at a temperature lower than the melting temperature of the olefinic resin. By this stretching, it is possible to produce voids in the substantially voidless layer, and there can be obtained a synthetic paper whose section has a porous structure throughout, and the void size differs from the surface layers to the inner layer.

The stretching temperature in the second method can be prescribed in the same way as set forth above with respect to the first method, and the same stretching operations and ratios can be employed.

The stretched sheets obtained in accordance with the above-mentioned embodiments can be directly used in 6 various applications such as printing, writing, or packaging. The sheets may be post-treated to improve the surface characteristics further.

The post-treatment can be performed, for instance, by heat-treating the stretched sheet at a temperature lower than the melting temperature of the olefinic resin under a tension which allows the shrinkage of the sheet. The term under a tension which allows the shrinkage of the sheet means the exclusion of a completely relaxed condition of the sheet. Specifically, it is preferred that the sheet be shrunk under a tension such as not to loosen the sheet, namely while sliding a sheet-holding device in follow-up of the shrinkage of the sheet. The shrinkage of the sheet may be at least 1 percent of the dimension before shrinkage. If the sheet is shrunk 2 to 10 percent, printability with an oily ink or graphic properties with a writing instrument become better, and the surface smoothness and luster also increase. The temperature needed for shrinking is below the melting temperature of the olefinic resin. Too low temperatures require long time to complete the shrinkage,

and therefore, it is convenient that the temperature is as near as possible to the melting temperature. The shrinking-temperature can be prescribed by any conventional means such as hot air, infrared heater,,water or oil bath. v

Another method of post-treating the stretched sheet involves subjecting the sheet to calender rolling with or without prior impregnation of a dispersion or solution of a thermoplastic resin such as styrene resins, polyvinyl resins, vinyl acetate resins, polyacrylate resins, or polyamide resins, or of a thermosetting resin such as phenolic resins, urea resins, melamine resins, or ketone resins. The calendering can be performed at a temperature lower than the melting temperature of the olefinic resin with a pressure between rolls being maintained at 10 kg/cm to kglcm preferably 30 kg/cm to 60 kg/cm. By this calendering, the voids on the surface layers of the stretched sheet become finer and denser, and the printability and graphic properties of the sheet are even more improved. In addition, the calendered sheet has superior stiffness, surface luster, surface smoothness and surface strength.

The synthetic paperobtained by the process of the present invention has a porous inner layer and porous surface layers, in which the void size differs from the inner layer to the surface layers and the void size distribution is symmetrical with respect to the center of the sheet. The synthetic paper of the invention has a lower density, lighter weight and better non-transparency than the conventional olefinic resin sheets of porous structure. Furthermore, it is excellent in physical strengths such as tensile strength, tear strength, and bending strength, and in graphic properties with a writing instrument, typographical properties with stamps or typewriters, or printability with a printing ink.

The synthetic paper obtained by the process of the invention also has good water resistance, and is suitable for uses which require water resistance.

The synthetic paper obtained by the present invention are therefore suitable as packaging materials with beautiful multicolor printing, printing papers for posters, picture books, books, orclalendars, wrapping materials for general use, cushion materials, air-permeable packaging materials. This sheets are particularly suitable for use in a dictionary printing. It is also useful as notebook paper or drawing paper which require graphic properties.

The synthetic paper of the invention also finds utility as building or decorative materials for use in walls,

size distribution is symmetrical with respect to the center line of a section of the sheet. The stretched sheet was superior in whiteness and non-transparency, and had a density of 0.665 g/cm roofs, and ceilings and also as agricultural or horticultur l aterials for us in reenhouses for instance.

a e g EXAMPLES 2 TO 16 Varlous uneven patterns can be lmparted to the synthetic paper obtained by the process of the invention by A 0.5 mm-thlck stretched sheet of an olefinlc resm embossing, and other synthetic resins can be adhered was formed in a manner similar to that set forth 1n Exthereto by thermal treatment. Such processed synthetic l0 ample l, and stretched at the same ratio both longitudipaper can be used for instance as materials of book nally and transversely at a rate of 100 cm per mlnute. binding or bag making. The stretched sheet obtained had small density and was The following Examples will further illustrate the light in w ightt als had g d n np y, present invention. Unless otherwise specified, all parts smoothness and physical strengths, and also good printin the Examples are parts by weight. ability such as ink setting and drymg properties.

In the Examples, the density and tensile strength of Microscopic photograph of the section of each of the the Sheet and the melting temperature of the olefini resulting sheets indicated that both the lnner layer and resin were measured in accordance with the followin the surface layers have a porous structure, the void slze methods. of the surface layers is smaller than that of the inner Density Dividing the weight in r ms of th h t layer, and the void size distribution is symmetrical with per centimeter by the thickness of the sheet in cenrespect to the center of the section of the sheet section. timeter (unit g/cm The results are given in Table l.

TABLE Stretching conditions Melting temper- Temper- Temper- Stretch ature ature ature ratio of the of the of the (X in olefinic surface inner one Examples resin layers layers direc- Density Nos. Composition of unstretched sheet C.) 0.) 0.) tion) (g./cm.

2 Low pressure polyethylene 126 120 100 3 0. 655 3 Low pressure polyethylene (100 parts) chlorinated polyethylene (5 parts) 126 120 100 3 0.638 4.. Low pressure polyethylene (100 parts) chlorinated polyethylene (10 parts) 126 120 100 3 0.625 126 100 80 3 0.603 Low pressure polyethylene (100 parts) silica powder (10 parts) 126 120 100 3 0. 620 Low pressure polyethylene (100 parts) chlorinated polyethylene (10 parts) silica 125 120 100 3 0.613

powder (10 parts). 8 Low pressure polyethylene (100 parts) polybutadiene (10 parts) 126 120 100 3 0.623 ll .do 126 125 110 1. 5 0. 785 10 .do 126 80 60 5 o. 375 11 Polypropylene resin 174 130 110 3 0.628 12. Polypropylene (100 parts) chlorinated polyethylene (10 parts) 174 130 110 3 0.618 13. Polypropylene (100 parts) polybutadiene (10 pa 174 130 110 3 0.610 14. Polypropylene (100 parts) silica powder (10 parts 174 130 110 3 0. 61C 15. Polyrzrppylene (100 parts) silica powder (10 parts) chlorinated polyethylene (10 174 130 110 3 0.593

par 5 16 Polypropylene (100 parts) polybutadiene (10 parts). 174 130 110 1.5 0.758

Tensile strength ASTM-D-638, at a pulling rate of EXAMPLE 17 50 mm/min. Meltin t m rature T -2l17 Pans g e pe As M D Low pressure polyethylene 100 (Hizex 6100 P) EXAMPLE 1 Ethylene/ vinyl acetate 30 co ol mer Evaflex No. 40,

Low pressure polyethylene resln (l-llzex 6100 P, g g g product of product of Mltsul Chemical Co., Ltd.) (having a melt- Mitsui Polychemical, Co., Ltd.)

Polystyrene resin (Sekisui l0 ing temperature of 120C.) was kneaded by a kneading roll heated to 150C. the kneaded polyethylene was formed into a sheet having a thickness of 0.5 mm by a heat press heated at 180C. The sheet was cooled to room temperature. Thereafter, the entire sheet was maintained at 80C., and then passed twice through heated rolls whose surfaces were maintained at 124C. The surfaces of the sheet were heated at 124C., but the inner layer of the sheet was maintained at 80C. by adjusting the rate of delivery of the sheet through the rolls to 12.0 meters per minute.

The sheet was then stretched at the above tempera ture to 2.5 times its original length both in the longitudinal and transverse directions. The stretching rate was adjusted to 100 cm per minute. Microscopic photograph of the section of the stretched sheet indicated that the inner layer and the surfaces layers have a porous structure, the voids size of the surface layers is smaller than that of the inner layer, and that the void Polystyrol HH-SOO, product of Sekisui Kagaku Kogyo K.l(.) Titanium oxide 3 Zinc sulfide/barium 7 sulfide mixture Silica powder The foregoing ingredients (the melting temperature of the olefinic resin being 126C.) were kneaded for 20 minutes at 150C. by a kneading roll, and formed into a sheet having a thickness of 0.5 mm by a kneading roll. The sheet was cooled down to room temperature, and the entire sheet was then maintained at C. The sheet was then passed twice through heated rolls whose surfaces were maintained at C. The surfaces of the sheet were heated to 120C., but the inner layer of the sheet was maintained at about 80C. by adjusting the rate of feeding the sheet between the heated rolls to 11.5 meters per minute.

The sheet was then stretched 2.5 times its original length both in the longitudinal and transverse directions.

Microscopic photograph of the section of the stretched sheet indicated that both the inner layer and the surface layers have a porous structure, the void size of the surface layers is smaller than that of the inner layer, and the void size distribution is symmetrical with respect to the center line of a section of the sheet. The stretched sheet had a density of 0.595 g/cm.

Printability test was performed on the resulting stretched sheet. It was found that the stretched sheet obtained in this Example has the same ink setting and drying properties as the commercially available art paper, and multicolor printing can be made on it. Thus, the stretched sheet obtained above was excellent in whiteness, non-transparency, smoothness, and physical strengths, and could be conveniently used as printing paper and wrapping paper.

EXAMPLE 18 parts Low pressure polyethylene 50 (Hizex 6100 P) High pressure polyethylene S (Sumikathene F-lOl-l, product of Sumitomo Chemical Co., Ltd.) Styrene-vinyl acetate copolymer 30 (Sumitate KC-lO, product of Sumitomo Chemical Co., Ltd.) Phenoxy resin (PAHJ, tradename 15 of the product of Union Carbide Co oration Kao in 20 Silica powder 20 Titanium oxide A composition comprising the foregoing ingredients (the olefinic resins having a melting temperature of 126C.) was kneaded for 15 minutes at 160C. by a kneading roll, and formed into a sheet having a thickness of 0.5 mm by calender rolling. The sheet was cooled to room temperature, and then the entire sheet was maintained at 80C. The sheet was subsequently passed twice through heated rolls whose surfaces were maintained at 100C. The rate of feeding the sheet between the heated rolls was adjusted to 12.0 meters per minute. The sheet was stretched to 2.5 times the original length both in the longitudinal and transverse directions.

Microscopic photograph of the resulting stretched sheet indicated that both the inner layer and the surface layers have a porous structure, the void size of the surface layer is smaller than that of the inner layer, and the void size distribution of is symmetrical with respect to the center line of a section of the sheet. The stretched sheet had a density of 0.580 g/cm The sheet so obtained was good in whiteness, non-transparency, smoothness, and physical strengths. Printability test indicated that the sheet obtained in this Example has better ink setting and drying properties than the commer-- cially available art paper. Moreover, multicolor printing could be made on it, and the sheet proved suitable as printing paper and wrapping paper.

EXAMPLE 19 parts Low pressure polyethylene 100 (Hizex 6100 P) Ethylene/vinyl acetate copolymer (Ultrathene 631, tradename of the product of Mitsui Polychemical Co., Ltd.) Polystyrene (Sekisui Polystyrol 10 HH-SOO, tradename of the product of Sekisui Kagaku Kogyo K.K.)

A composition of the foregoing ingredients (the olefinic resin having a melting temperature of 126C.) was kneaded for 15 minutes by a kneading roll heated at 160C., and formed into a sheet having a thickness of 0.5 mm by calender rolling. The sheet was cooled to room temperature, and then the entire sheed was maintained at 80C. The sheet was then passed twice through heated rolls whose surface temperatures were maintained at 120C. The rate of feeding the sheet between the heated rolls was adjusted to 12.0 meters per second. The sheet was then stretched to 2.5 times its original length both in the longitudinal and transverse directions.

Microscopic photograph of the stretched sheet obtained indicated that both the inner layer and the surface layers have a porous structure, the void size of the surface layers is smaller than that of the inner layer, and the void size distribution is symmetrical with respect to the center line of a section of the sheet. The sheet had a density of 0.583 g/cm.

The stretched sheet so obtained was excellent in whiteness, non-transparency, smoothness and physical strengths. Printability test indicated that it has better ink setting and drying properties than the commercially available art paper. Multicolor printing could be made on it, and the sheet proved useful as printing paper and wrapping paper.

EXAMPLE 20 parts Medium low pressure polyethylene (Staflene tradename of the product of Furukawa Chemical industry, Co.', Ltd.) Styrene/vinyl acetate 10 copolymer (Ultrathene 631) Polybutadiene (JSR-B-R-Ol, 20 tradename of the product of Japan Synthetic Rubber Co., Ltd.) Polystyrene l0 (Sekisui Polystyrol HH-500) Diatomaceous earth 30 Titanium oxide 5 Zinc sulfide/barium sulfate. 10 mixture A composition consisting of the foregoing ingredients (the olefinic resin having a melting temperature of 129C.) was kneaded for 15 minutes by a kneading roll heated at 150C., and formed into a 0.5 mm thick sheet by calender rolling. The sheet was cooled to room tem perature, and the entire sheet was maintained at 80C. The sheet was then passed twice between heated rolls whose surfaces were maintained at C. The rate of feeding the sheet between the heated rolls was adjusted to 12.0 meters per minute. The sheet was then stretched to 2.5 times its original length both in the longitudinal and transverse directions.

Microscopic photograph of the stretched sheet obtained indicated that both the inner and surface layers have a porous structure, the void size of the surface lay- The stretched sheet so obtained was excellent in whiteness, non-transparency, and physical strengths. Printability test indicated that the sheet obtained above has better ink setting and drying properties than the commercially available art paper. Multicolor printing could br made on it, and the sheet proved useful as printing paper and wrapping paper.

EXAMPLE 21 Low pressure polyethylene resin (Hizex 6100 P) (having a melting temperature of 126C.) was kneaded by a kneading roll heated at 150C, and formed into a 0.5 mm thick sheet by a heat press heated at 180C. The sheet was cooled to room temperature, and the entire sheet was maintained at 125C. The sheet was passed twice through water cooled rolls whose surfaces were maintained at 20C.

The temperature of the inner layer was maintained at 125C., but the surface layer of the sheet was maintained at about 80C. by adjusting the rate of moving the sheet between the cold rolls to 12.0 meters per minute. The sheet was then stretched to 2.5 times the original length both in the longitudinal and transverse directions.

Microscopic photograph of the section of the stretched sheet obtained indicated that both the surface and inner layers have a porous structure, the void size of the surface layers is larger than that of the inner layer, and the void size distribution is symmetrical with respect to the center line of a section of the sheet. The sheet was excellent in whiteness and non-transparency, and had a density of 0.645 g/cm.

EXAMPLES 22 TO 34 Each of the olefinic resin compositions indicated in Table 2 was formed into a 0.5 mm thick sheet in a manner similar to that set forth in Example 21. The resulting sheet was stretched at a rate of 50 cm per minute at the same ratio both in the longitudinal and transverse directions under the stretching conditions shown in Table 2. The resulting stretched sheet had a small density, and therefore was light in weight. It was excellent in non-transparency and physical strengths, and had good printability such as ink setting and drying properties.

Microscopic photograph of the section of the sheet indicated that both the surface and inner layers have a porous structure, the void size of the surface layer is larger than that of the inner layer, and the void size dis- EXAMPLESS An unstretched sheet produced in the same way as set forth in Example 17 was maintained at 125C., and passed twice through water cooled rolls whose surfaces were maintained at 20C. At this time, the inner layer of the sheet was maintained at 125C., and the surface layers were maintained at about 80C. by adjusting the rate of moving the sheet on the cooled rolls to 12.0 meters per minute. The sheet was then stretched to 2.5 times its original length both in the longitudinal and transverse directions. 5

Microscopic photograph of i the section of the stretched sheet indicated that both the surface and inner layers have a porous structure, the void size of the surface layer is larger than that of the inner layer, and the void size distribution is symmetrical with respect to the center line of a section of the sheet. The stretched sheet obtained had a density of 0.598 g/cm.

The stretched sheet obtained was subjected to the printability test, and it was found that it has good printability such as'ink setting and drying properties. Multicolor printing could be made, on it. The sheet obtained also i had excellent whiteness, non-transparency, smoothness, physical strengths, leather-like feel, and stiffness and feel similar to those of paper made of a material of natural origin, and were useful as printing paper and wrapping paper.

EXAMPLES 36 TO 40 Each of the resin compositionsshown in Table 3 was formed into an unstretched sheet in the same manner as shown inExample 17, and stretched under the same conditions as given in Example 35. The stretched sheet had similar properties as those of the stretched sheet obtained in Example 35.

TABLE 3 (Sekisui Polystyrol l-lH-SOO) Titanium oxide 5 tribution 1S symmetrical with respect to the center lme Diammaceous earth 30 of a section of the sheet. Calcium carbonate 20 TABLE 2 Stretching conditions Melting tempcr- Temper- Temper- Stretch aturo aturc atnre ratio of the of the of the (X in l mmpm olefirnc sprface linner one resin a ers a r 0s. Composition of unstrctched sheet 0.) C.) if) lib?) 22. Low pressure polyethylene 126 100 120 3 0. 648 23 d0 126 120 3 0.623 :34 Low pressure polyethylene parts) chlo nated polyethylene (5 parts)- 126 100 120 3 0. 635 ..t10 126 60 100 3 0.618 ;(i. 126 100 120 l. 5 0. 780 -7-. ..do 126 100 120 6 0.383 28- Low pressure polyethylene (100 parts) sihca powder (10 parts). 126 100 120 3 0. 628 29- Polypropylene (100 parts) 174 140 3 0.630 30- .do 174 60 3 0. 608 31. Polypropylene (100 parts) polybutene (5 parts) 174 110 3 0.633 32- do- 174 60 120 3 0. 588 33- do. 174 110 140 1. 5 0. 748 34. do. 174 110 140 6 0.365

37 Low pressure polyethylene 100 126 0.595

(Hizex 6100P) Ethylene/vinyl acetate 10 copolymer (Ultrathene 631) Polystyrene resin 10 (Sekisui Polystyrol HHSOO) Styrene/butadiene copolymer 20 14-101, tradename of the product of Shell Chemical) Powdery silica 40 Titanium oxide 5 38 Medium low pressure 50 129 0.604

polyethylene resin (Staffene E-603, tradename of the product of Furukawa Chemical lndustry Co., Ltd.)

High pressure polyethylene 50 resin (Sumikathene F-ll-l, tradenamr of the product of Sumitomo Chemical) 38 Ethylene/vinyl acetate 30 copolymer (Evaffex No. 40)

Polystyrene resin 15 (Sekisui Polystyrol HH-500) Kaolin 25 Diatomaceous earth 25 Titanium oxide 7 39 Low pressure polyethylene 100 130 0.600

(Hizex 5300 B, tradename of the product of Mitsui Chemical) Ethylene/vinyl acetate 10 Copolymer (Ultracene 631) Polybutadiene (JSR-B-R-Ol, 20 Japan Synthetic Rubber Co.,

Ltd. Polystyrene (Denka Styrol l0 Hl-E-2, product of Denki Kagaku Kogyo K.K.)

Silica powder 30 Titanium oxide Zinc Sulfide/barium sulfate l0 mixture 40 Polybutene resin (polybutene 100 I35 0.590 BT, Huls Corporation) Polybutadiene (.lSR-BR-Ol) Styrene/butadiene 20 copolymer (K-lOl) I Polyacetal resin 10 (Duracon, Polyplastics Corp.)

Kaolin 2O Diatomaceous earth 20 Titanium oxide 7 EXAMPLE 41 Parts by weight Polypropylene resin (Chisso 100 Polypro I014, Chisso Corporation) Polypropylene resin 10 (Vista! CC, Chisso Corporation) Phenoxy resin (PAHJ, Union l0 Carbide Corporation) Polybutadiene (Dienerubber. 20 Asahi Kasei Kogyo K. K.) Diatomaceous earth 20 Silica powder 2 Titanium oxide 7 A composition of the foregoing ingredients (the olethe void size distribution is symmetrical with respect to the center line of a section of the sheet.

The stretched sheet so obtained was excellent in whiteness, non-transparency and physical strengths, and the printability test indicated that it has good ink setting and drying properties. The surface of the sheet had appearance and feel like those of leather.

EXAMPLE 42 High density polyethylene (Hizex 6100 P) (having a melting temperature of 126C.) was kneaded by a kneading roll heated at 150C., and formed into a 0.5 mm thick sheet by a heat press heated at 180C. The sheet was cooled to room temperature, and then the entire sheet was heated to 80C. The sheet was passed four times through rolls whose surface were maintained at 110C. Immediately thereafter, the sheet was stretched to 3 times its original length both in the longitudinal and transverse direction at a rate of 60 cm per minute. The temperature of the sheet was 110C., and

' cated that both the inner and surface layers have a pofinic resin having a melting temperature of 174C.) was kneaded for 15 minutes by a kneading roll heated at 180C., and formed into a 0.5 mm thick sheet by calender rolling. The sheet was cooled to room temperature, and then maintained at a'temperature of 170C. for 5 minutes. The sheet was then passed twice through cooled rolls whose surfaces were maintained at 60C. The surface of the sheet was maintained at 100C. The rate of moving the sheet on the cooled rolls was adjusted to 12.0 meters per minute. The sheet was then stretched to 3.0 times its original length both in the longitudinal and transverse directions at a rate of cm per minute.

Microscopic photograph of the section of the resulting stretched sheet indicated that both the surface and inner layers have a porous structure, the void size of the surface layer is larger than that of the inner layer, and

rous structure, the void size of the surface layer is smaller than that of the inner layer, and the void size distribution is'symmetrical with respect to the center line of a section of the sheet. The resulting sheet had a density of 0.638 g/cm.

The sheet so stretched was then cooled to room temperature, and maintained at 120C. The sheet was then further stretched to 1.8 times its original length both in the longitudinal and transvere directions at a rate of 50 cm per minute. Microscopic photograph of the section of the resulting sheet indicated that the voids in the surface layers are finer and denser. The sheet was excellent in whiteness and non-transparency, and had a density reduced to-0.520 g/cm When each of the stretched sheets obtained in Examples 17 to 20 was further stretched under the same conditions as set forth above, there was obtained a synthetic paper having improved surfacecharacteristics and reduced density. The resulting sheet further stretched had excellent whiteness, non-transparency, smoothness and physical strengths. The printability test indicated that the synthetic paper has better printability such as ink setting and drying properties than commercial available art paper. Multicolor printing could be made on it, and the synthetic paper proved useful as printing paper and wrapping paper.

' EXAMPLES 43 TO 57 a Each of the resin compositions shown in Table 4 was formed into a 0.5 mm thick unstretched sheet in the same way as set forth in Example 42. The sheet was stretched under the primary stretching conditions at 60 the ratio indicated both in the longitudinal and transoriginal length both longitudinally and transversely at a rate of 100 cm per minute.

Microscopic photograph of the section of the resulting stretched sheet indicated that both the surface and inner layers have a porous structure, the void size of the surface layer is smaller than that of the inner layer, and the void size distribution is symmetrical with respect to the center line of a section of the sheet. The stretched alum Primary stretching conditions Melting temper- Temper- Temper- Stretch Composition of unstretched sheet ature atnre ature ratio of the of the of the (X in Amounts olefiuic surface inner one in parts resin layer layer direc- Exmnples Nos. Ingredients by weight C.) C.) C.) tion) 43 Low pressure polyethylene 126 120 100 3 44 Low pressure polyethylene 100 126 100 80 2 Chlorinated polyethylene 45 Low pressure polyethy1ene Chlorinated polyethylene 46 Low pressure polyethylene.

Chlorinated polyethylene Silica powder 47 Low pressure polyethylen Chlorinated polyethylene Silica powder 48 Low pressure polyethylene-..

Chlorinated polyethylene 49 Polypropylene Polypropylene... Poiybutadiene-- 51 Polypropylene...

Polybutadiene.. 52 Polypropylene Chlorinated polyethylene- 53 Polypropylene Silica powder..... 54 Polypropylene Chlorinated polyethylene. Silica powder 55 Polypropylene Chlorinated polyethylene Silica powder 56 Polypropylene Chlorinated polyeth Silica powder 57 Polypropylene--.

Chlorinated polye ylen Silica powder Secondary I Density 4O 3 Density of Stretch ofthe sheet had a density of 0.675 g/cm d the primarily ing conditions secondarily The sheet was then cooled to room temperature, an E p g z i pf slrelchhed then maintained at C. The sheet was stretched furos.

i s mm f fi ther to 1.5 times its primarily stretched length both in 23 0.345 1.5 0.536 the longitudinal and transverse directions at a rate of 4. 2.5: 1:: :5 2522 1 permfinute- 46 0.595 115 1.5 0.463 Microscopic photograph of the resulting stretched Z; 8-2;; g-Z g sheet indicated that its surface characteristics have 49 0:628 1:5 0:485 been further improved, and an innumerable number of 50 0-623 130 0470 small cracks are formed among the voids that make up 51 0.618 130 1.5 0.463 59 th V t f th f Th t t h d 52 0520 130 L5 0465 e porous struc ure 0 e sur aces. e s re 9 e 53 0.605 130 1.5 0.442 sheet had excellent whiteness and non-transparency, i; g'ggg 3 gig; and had a density of 0.540 g/cm. 56 0.575 120 1.5 0.422 Each of the primarily stretched sheets produced in 57 L2 0708 Examples 17 to 20 was subjected to a secondary 55 i EXAMPLE 58 stretching under the same conditions as mentioned Low pressure polyethylene resin (Hizex 6100 P) (having a melting point of 126C.) was kneaded by a kneading roll heated at C, and formed into a 0.5 mm thick sheet by a heat press heated at C. The sheet was cooled to room temperature, and then the entire sheet was maintained at 10C. The sheet was then passed four times through heated rolls whose surfaces were maintained at 125C. The surface of the sheet was heated at 125C., and the temperature of the inner layer was maintained at about 100C. by adjusting the rate of moving the sheet on the rolls to 12.0 meters per minute. The sheet was stretched to 3 times its above. By this stretching, there was obtained a syntheticpaper having more improved surface characteristics and reduced density.

EXAMPLES 59 TO 73 Each of the olefinic resin composition shown in Table 5 was formed into a 0.5 mm thick unstretched sheet in the same way as set forth in Example 58. The sheet was stretched at a rate of 100 cm per minute under the primary stretching conditions given .in Table 5. The resulting sheet was cooled to room temperature, and then further stretched at a rate of 50 cm per minute under the second stretching conditions shown in Table 5. Microscopic photograph of the section of the sheet so stretched indicated that both of the inner and surface layers have a porous structure, the void size of the surface layers is smaller than that of the inner layer,

rolls whose surface were maintained at 80C. Immediately after passage, the sheet was stretched to 3 times its original length both in the longitudinal and transverse directions at a rate of 100 cm per minute. The

and the void size distribution is symmetrical with re- 5 Surfaces f th h t were ooled at this time to 80C. p c to the ce e of a S i n O t e Sheet- An But the temperatureof the inner layer was maintained numerable number of small cracks formed bythe sect ab ut 120C. by feeding the sheet between the rolls n ry r ching ere pr sen in the rface l yer ata rate of 12.0 meters per minute. Microscopic photoand this led to the confirmation that very fine and -graph of the section of the sheet indicated that both the dense Voids were formed in the Surface ye The surface and inner layers have a porous structure, the sheet so obtained had low density and was light in void size of the surface layer is larger than that of the weight. it had excellent non-transparency, smoothness, inner layer, and the void size distribution is symmetriand physical strengths, and also good printability such cal with respect to the center of the section of the as ink setting and drying properties. sheet. The stretched sheet had a density of 0.643 g/cm.

TABLE 6 i Hw Primary stretching conditions Melting y temper- Temper- Temper- Stretch Composition of nnstretched sheet ature ature ature ratio of the of the of the (X in Amounts oleflnic surface inner one in parts resin layer layer direc- Examples Nos. Ingredients by weight C.) C.) 0.) tion) Low pressure polyethylene... Low pressure polyethylene.

Chlorinated polyethylene... Low pressure polyethylene. Chlorinated polyethylene. Low pressure polyethylene... Chlorinated polyethylene. Silica powder Low pressure polyethylene..-. Chlorinated polyethylene. Silica powder Polypropylene- Poiybutadiene. Polypropylene Chlorinated polyethylene. Polypropylene Silica powder. Polypropylene. Chlorinated polyethylene Silica powder.

Polypropylene Chlorinated polyethyle Silica powder Polypropylene Chlorinated polyethylene. Silica powder Polypropylene Chlorinated polyethylene.

Secondary Density of stretch- .of the the primarily ing conditions secondarily Example stretched Temp. Stretch stretched Nos. sheet (C.) ratio sheet (g/ (it/ 59 0.658 80 1.5 0.548 60 0.635 80 1.5 0.535 6! 0.625 80 L5 0.523 62 0.610 80 L5 0.496 63 0.602 80 1.5 0.472 64 0.605 80 1.5 0.478 65 0.638 I00 1.5 0.465 66 0.620 90 L5 0.433 67 0.6i0 90 1.5 0.425 68 0.623 90 1.5 0.430 69 0.607 90 1.5 0.45 70 0.605 90 L5 0.4l8 7i 0.595 90 L5 0.40 72 0.595 1.5 0.385 73 0.595 1.2 0.495

EX A M PLE 74 Low pressure polyethylene resin (Hizex 6l00 P) was kneaded by a kneaded roll heated at i50C., and formed into a 0.5 mm thick sheet by a heat press heated at 180C. The sheet was cooled to room temperature, and then the entire sheet was heated to a temperature of C. The sheet was then passed fourtimes through batter 0 The sheet was then cooled to room temperature, and then the entire sheet was maintained at 80C. The sheet was stretched secondarily to 1.5 times its primarily stretched length both in the longitudinal and transverse directions at a rate of 50 cm per minute. Microscopic photograph of the resulting sheet indicated that the surface characteristics of the sheet are more improved, and the surface layers have a fine and dense, porous structure. The sheet so obtained had excellent whiteness and non-transparency. It had high stiffness, and exhibited a leather-like feel and appearance. The density of the sheet .was 0.545' g/cm.

Each of the primarily stretched sheets produced in Examples 36 to 41 was further stretched under the conditions mentioned above. There was obtained a synthetic paper having more improved surface characteristics and reduced density. Such stretched sheet had excellent whiteness, non-transparency, and physical strengths. It had high stiffness and exhibited a leatherlike feel and appearance at the surface. The printability test indicated that it has good printability such as ink setting and drying properties. Multicolor printing could proved useful as wrapping paper or papers for building material such as wall paper.

Examples 75 TO 87 Each of the olefinic resin compositions shown in Table 6 was formed into a 0.5 mm thick unstretched sheet in the same manner as set forth in Example 74, and stretched at a rate of I cm per minute under the primary stretching conditions as shown in Table 6. The sheet was then cooled to room temperature, and further stretched at a rate of 50 cm per minute under the secondary stretching conditions shown in Table 6.

Microscopic photograph of the section of the resulting sheet indicated that both the inner and surface layers have a porous structure, the void size of the surface layer is larger than that of the inner layer, and the void size distribution is symmetrical with respect to the center line of a section of the sheet. It was also confirmed that very fine and dense voids were formed on the sur-- then the entire sheet was heated again to llC. The sheet was passed four times through heated rolls whose surfaces were maintained at 80C. at a rate of 12.0 meters per minute. Immediately after passage, the sheet was stretched to 3 times its original length both in the longitudinal and transverse directions at a rate of 60 cm per minute. The sheet so stretched had a density of 0.638 g/cm. The resulting sheet was cooled to room temperature, heated to a temperature of 125C., and stretched to 1.8 times its primarily stretched length both in the longitudinal and transverse directions at a rate of 50 cm/min. Microscopic photograph of the section of the stretched sheet indicated that the void size of the surface layers is larger than that of the inner layer, and the void size distribution is symmetrical with respect to the center line of a section of the sheetylt was also found that voids which are finer and denser than the voids in the surface layers formed by the primary stretching are produced in the surface layer. The surfaces were of very fine and dense porous structure. The stretched sheet had excellent whiteness and nontransparency and good printability, and had a density of 0.5l0 g/cm.

TABLE 6 Q Primary stretching conditions Melting temper- Temper- Temper- Stretch Composition of unstretehed sheet ature ature ature ratio of the of the of the (X in Amounts olefinie surface inner one in parts resin layer layer direc- Exemplos Nos. Ingredients by weight 0.) 0.) 0.) tion) Low pressure polyethylene 126 100 120 3 Low pressure polyethylene 126 80 120 3 Low pressure polyethylene 100 126 100 120 3 Chlorinated polyethylene 5 Low pressure polyethylene..... 100 126 60 100 3 Chlorinated polyethylene 5 Low pressure polyethylene 100 126 100 120 3 Polybutadiene 6 80. Low pressure polyethylene... 100 126 100 120 3 Polybutadlene 5 Silica powder. 10 Polypropylene. 174 120 140 3 Polypropylene. 100 174 110 130 3 Chlorinated polyethylene 6 Polypropylene 100 174 110 130 3 Polybutadiene 5 Polypropylene-.. 100 174 110 130 3 Silica powder. 10 Polypropylene 100 174 80 100 3 Polybutad1ene 5 Polypr0pylenc. 100 174 80 100 5 Polyhutadlene 5 Pol ypropylonc. 100 174 140 150 1. 8 Polybutadlene 5 D r Secongiary Derfrsig Each of the primarily stretched sheets produced in CD3] y 0 SU'CIC O t e the primarily ins conditions the secondarily Examples to 41 was secondarily stretched under the Example stretched Temp, str t h stretched same cond1t1ons as descrlbed above- The resulting syn- F 2 thetic paper had more improved surface characteristics 0.648 100 1.5 0.568 and reduced i y- 76 0.643 I00 l.5 0.533 0.635 80 L5 0.530 0.6 it 80 L5 0.525 E P 7 0.623 80 1.5 0.525 55 XAM LES 89 To 101 N0 0.618 80 l.5 g 0,510 g; 108 1.5 0.470 Each of the olefinic resin compositions shown in 83 0:625 {8 3:222 Table 7 was formed into a 0.5 mm thick unstretched g t 0.610 1.5 0.433 Sheet, and stretched at a rate of 60 cm/min. under the 0.590 80 L5 0.427 86 0398 80 25 0350 60 pr1mary stretching cond1t1ons g1ven 1n Table 7. The 87 0.730 1.2 0.713 sheet was cooled to room temperature, and then stretched at a rate of 50 cm er minute under the sec- EXAMPLE 88 p ondary stretching conditions shown in Table 7. The microscopic photograph of the section of the sheet indicated that both the surface and inner layers have a porous structure, the void size of the surface layer is larger than that of the inner layer, and the void size distribution is symmetrical with respect to the center line of a section of the sheet. it was also confirmed that voids which are finer and denser than the voids formed in the surface layers by the primary stretching were produced in the surface layers. The resulting sheet had a small density, and therefore was light in weight. It had excellent non-transparency, smoothness, and physical properties and good printability such as ink setting and drying properties.

tween the rolls to 12.0 meters per minute. The inner layer of the resulting sheet had a porous structure, and voids were not formed on the surface. The sheet had a density of 0.758 glcm The sheet was then cooled to room temperature, and then maintained at a temperature of l C. Subsequently, the sheet was stretched to 1.5 times its original length at a rate of cm/min. both in the longitudinal Tli'iiiii? Primary stretching conditions Melting temper- Temper- Temper- Stretch Composition of unstretehed sheet ature ature ature ratio of the of the of the (X in Amounts olefinic surface inner one in parts resin layer layer direc- Examples Nos. Ingredients by weight C C.) C 0.) tion) so 126 100 120 3 90.- 126 so 120 a 91-. 126 100 a .12 --do 126 so 115 3 Chlorinated polyethylene 5 Low pressure polyethylen 100 126 60 3 Chlorinated polyethylene. 5 Low pressure polyethylen 126 80 1. 8 Chlorinated polyethylene... 5 Low pressure polyethylene.. 100 126 80 115 6 Chlorinated polyethylene- 5 Low pressure polyethylene" 100 126 80 3 Polybuta 5 Low pressure po1yethy1ene.- 100 126 80 3 I Silicia pow er 10 Polypropylene.. 100 174 3 0o ..do 100 174 110 3 Poiybutadiene 5 100 Polypropylene 100 174 110 1.8 Polybutadiene 5 101 Polypropylene v 100 174 110 a 6 Polybutadiene 5 D 1 f 51 3") and transverse directions. The microscopic photograph ensiyo sreco e the primarily ing conditions secondarily of the resulting sheet ind cated that fine and dense Example stretched Temp. Stretch stretched voids are formed from the inner layer towards the sur- 372; (OC') "1 72:5; 35 face layers, and the surface also has a fine and dense, 89 0.648 125 1.5 0.531s porous structure. The resulting sheet had unique luster, 3? ggg 3-2: and excellent whiteness, non-transparency, smoothness 3% 0:630 25 5 @1503 and physical strengths. The density of the sheet was 0.565 1 120 1.5 0.475 0.560 cm 3g 125 1.2 0.735 40 g/ 125 2.0 0.305 96 0.620 125 1.5 0.5 0 XAMPLES 103 T0 114 g; 8'23; 8'23; Each of the olefinic resin compositions shown in 9 0.625 1.5 0:470 Table 8 was formed into a 0.5 mm thick sheet in the 100 0740 140 L2 0715 same manner as set forth in Exam le 102. The sheet 101 0.390 140 2 0.320 p EXAMPLE 102 Low pressure polyethylene resin (having a melting temperature of 126C. was kneaded by a kneading roll heated at C., and formed into a 0.5 mm thick sheet by a heat press heated at 180C. The sheet was cooled to room temperature, and the entire sheet was maintained at 100C. The sheet was then passed three times through rolls whose surfaces were maintained at C. Immediately after passage, the sheet was stretched primarily to 3 times its original length both in the longitudinal and transverse directions at a rate of 100 cm/min. The temperature of the surface of the sheet was heated to 160C, but the inner layer was maintained at about 100C. by adjusting the rate of feeding the sheet bewas stretched at a rate of 60 cm/min. There was obtained a smooth sheet having a porous inner layer and voidless surface layers.

The sheet was cooled to room temperature, and then stretched at 50cm/min. under the secondary stretching conditions as shown in Table 8. The microscopic pho tograph of the section of the resulting sheet indicated that both the inner and surface layers have a porous structure with fine and dense voids formed from the inner layer towards the surface layers. It was also confirmed that fine and dense voids are formed on the surface. The resulting sheet had low density, and therefore was light, in weight. It had excellent non-transparency, smoothness and physical strengths and good printabil ity such as ink setting and drying properties.

nitia s Primary stretching conditions Melting temper- Temper- Temper- Stretch Composition of unstretohed sheet ature ature ature ratio of the of the of the (X in Amounts olefinic surface inner one in parts resin layer layer direc- Examples Nos. Ingredients 1 by weight 0.) C.) C.) tion) Low pressure polyethylene. 126 160 110 3. 0 -d0 126 160 80 3. 0 105 .-d0 100 126 160 110 3.0 Chlorinated polyethylene 5 106 Low pressure polyethylene. 100 126 160 110 1. s

3,758,661 23 24 iTjijEii riominued h V Primary stretching conditions I 'temper- Tem er Composition ofunstretched sheet ature at izre 25598 Stretch ratio of the i of the of the (X in Amounts OIGfiIIiIC surface inner one ill 3 S I Examples Nos. Ingredients by w ig ht 53 63 M 3 37 iii r Chlorinated polyethylene .i o 107; Low pressure polyethylene .1 100 126 160 110 a. (1 Chlorinated polyethylene 103 Low pressure polyethylene 100 126 160 110 3. 0 Silica powder 10 109 Polypropylene 174 200 130 3.0 110 Polypropylene 100 174 200 130 3.0 Chlorinated polyethylene. 5 111 Polypropylene 100 174 200 130 3.0 Polybutadiene 5 112 Polypropylene 100 174 200 130 1. Polybutadiene 5 113 Poiypropylene.- 100 200 130 s 0 Polybutadiene. 5 114 Poiypropylene-- 100 200 130 e 0 Polybutadiene 6 Secondary 1 Density EXAMPLES 1 TO 120 Density of stretchof the 'the primarily ing conditions secondarily Example stretched sheet Temp. Stretch stretched Each of the resin composltions shown in Table 9 was 0 i ig :53; kneaded by a kneading roll mamtamed at l60C., and 103 H0 15 056g was fonned into a 0.5 mm thick sheet by calender roll- :g; 82;; H8 8-223 ing. The sheet was primarily stretched under the same 106 02799 no 0:735 1 conditions as set forth in Example 102. There was ob- 107 0.420 110 1.8 0.368 tained a sheet having a porous inner layer and voidless 108 0.740 110 1.5 0.538 rf pl 109 0.735 120 1.5 0.525 ace ayers' 110 7 5 20 1,5 0,435 The sheet was further stretched under the, same sec- 0720 0478 ondary stretching conditions as set forth in Example 112 0.759 H0 1.2 0.702 H3 0398 120 L8 0335 102 to form a sheet which also had fine and dense vo1ds 114 0.398 1.8 0.315 on the surface. The results are given in Table 9.

TABLE 9 l Melting tempera- Density Density of Composition of unstretehed sheet ture of of sheet the sheet the main after the after the Amount olefinic primary secondary in parts resin stretching stretching Example No. Ingredients v by weig t (el (g-lcfi) 115 Low pressure polyethylene 0 520 Ethylene/vinyl acetate eopolymer. Polystyrene resin Titanium oxide Diatomaceous earth. Calcium carbonate 116 Low pressure polyethylene Ethylene/vinyl actate copolymer Polystyrene Styrene/butadiene c I 1 Silica powder- Titanium oxide Polystyrene resin- Styrene/butadiene c Silica powder.

7 Titanium oxid 118. 1 1 Medium prossur High pressure polyethylene.

' Ethylene/vinyl acetate copolyme Titanium oxide. lliL. r N Low pressure poly Ethylene/vinyl copolymer Polybutndiene Titanium oxide Zinc sulfide/barium sulfate xture 1'20 i s Polybutene rosin Polybutmliene Styrene/butndiene eopolymer. Polyacctel resin v Kaolin Diatomaceou earth 1 Titanium oxide The sheets obtained in these Examples had good whiteness, non-transparency, smoothness and physical strengths. The printability test indicated that it has beeter printability such as ink setting and drying properties than the commercially available art paper. It proved useful as multicolor printed wrapping paper or papers for building or decorative materials.

EXAMPLE 121 Parts Polypropylene l Phenoxy resin 10 Polybutadiene Diatomaceous earth 20 Silica powder 20 Titanium 7 A composition of the foregoing ingredients (the polypropylene resin having a melting temperature of 174C.) was kneaded for 15 minutes by a kneading roll heated at 180C., andformed into a 0.5 mm thick sheet by a heater press. The sheet was cooled to room temperature, and then maintained at 120C. it was then passed three times through rolls whose surfaces were maintained at 200C., and immediately thereafter, stretched to 3 times its original length both in the longitudinal and transverse directions at a rate of 80 cm/min. The resulting sheet had a porous inner layer and voidless smooth surfaces and a density of 0.732 g/cm. The sheet was cooled to room temperature, and then heated to 140C. The sheet was stretched to 1.5 times the primarily stretched length at a rate of 50 cm/min. both in the longitudinal and transverse directions. Microscopic photograph of the section of the resulting stretched sheet indicated that tine and dense voids are formed from the surface layertowards the inner layer, and fine and dense voids are formed on the surface. The density of the resulting sheet was 0.508 g/cm. The stretched sheet so obtained had excellent whiteness, non-transparency, and physical strengths. The printability test indicated that it has good ink setting and drying propertiesvThe sheet obtained had stiffness, feel, printability and graphic properties like paper, and exhibited better printability such as ink setting and drying properties than the commercially available art paper. The sheet proved useful as printing paper, wrapping paper, and papers for use in building and decorative materials.

EXAMPLE 122 Low pressure polyethylene resin (having a melting temperature of 126C.) was heated by a kneading roll heated at l 50C., ad formed into a 0.5 mm thick sheet by a heat press heated at 180C. The sheet was cooled to room temperature, and the entire sheet was maintained at 160C. The sheet was then passed three times through rolls whose surfaces were maintained at 120C.

The surface of the sheet was cooled to 120C., but the inner layer was maintained at about 160C. by adjusting the rate of moving the sheet through the rolls to 12.0 meters per minute. Immediately thereafter, the sheet was stretched to 3.0 times its original length both in the longitudinal and transverse directions. Microscopic examination of the section of the stretched sheet indicated that the surface layers have a porous structure, and the inner layer is voidless. The density of the sheet was 0.770 g/cm". The sheet so obtained was.

cooled to room temperature, and then maintained at 120C. Thereafter, the sheet was stretched to 1.5 times the primarily stretched length at a rate of. 80 cm/min. both in the longitudinal and transverse directions. Microscopic photograph of the section of the stretched sheet indicated that both the surface and inner layers have a porous structure, and the void size of the surface layers differs from that of the inner layer. The sheet had luster and good whiteness, non-transparency and physical strengths. The density of the sheet was 0.563 g/cm.v

EXAMPLES 123 TO 125 Each of the olefinic resin "compositions shown in Table 10 was formed intoa 0.5 mm thick sheetin the same manner asset forth in Example 122, and stretched at 100 cm/min. under the primary stretching conditions shown in Table 10. The resulting sheet had poroussurface layers and a voidless inner layer like the primarily stretched sheet obtained in Example 122.

" TABLE 10 Primary stretching conditions Melting temper- Temper- Temper- Stretch Composition of unstretched sheet ature ature nre ratio of the of the of the (X in Amounts olefinic surface inner one i in parts resin layer layer direc- Examples Nos. Ingredients by weight 0.) C.) C.) tion) 128 Low pressure polyethylene 132 126 160 3. 0 124 Low pressure polyethy1ene-. 126 160 3. 0 Chlorinated polyethylene--. a Low pressure polyethylen 100 126 80 160 3. 0 Chlorinated polyethylene... i 5

Low pressure polyethylene 100 126 120 160 1.8

Chlorinated polyethylene. 5 Low pressure polyethylen I 100 126 120 160 6. 0

Chlorinated polyethylene 6 Low pressure polyethylen 100 126 120 160 3.0

Silica powder g 10 Polypropylene 174 200 3. 0

' 130.. ..do 100 174 140 200 3. 0 Chlorinated polyethylene 5 131 Polypropylene...- 100 174 140 200 3.0 Polybutadlene 5 132 Polypropylene" 100 174 140- 200 1. 8 Poly utadiene.. 5

133 Poly ropylone... 100 174 140 200 6.0 Poly utadiene 5 Polypropylene 100 174 140 200 6. 0

Polybutndiene Each of the resin compositions given in Table 11 below was kneaded by a kneading roll heated at 160C, formed into a 0.5 mm thick sheet by calender rolling, and then stretched under the same stretching conditions as set forth in Example 122. The resulting sheet had porous surface layers and a voidless inner layer. The sheet was further stretched under the same secondary stretching conditions as set forth in Example 122 to form a sheet in which the inner layer also had fine and dense voids. The results are given in Table l 1.

cm/min. both in the longitudinal and transverse directions. Microscopic examination of the section of the resulting sheet indicated that the inner layer is also porous. The resulting sheet had excellent whiteness, nontransparency and physical strengths. The surface of the sheet exhibited feed and appearance like those of leather. It had stiffness and printability comparable to paper from a material of natural origin. Such sheets to which gravure printing was applied proved useful as wrapping paper, cushion wrapping paper, and papers I for use in building and decorative materials.

EXAMPLE 138 Both ends of each of the stretched sheets obtained in Examples 1, 21, 42, 58, 88, 102 and 122 were fixed with a fixing device, and maintained at 120C. When the entire sheet shrank by percent, the sheet wasrapidly cooled. It was found that the shrunk sheet had a finer and denser porous structure and a moresmooth surface. The shrunk sheet exhibited stiffness and feel similar to those of paper from a material of natural origin, and proved useful as printing paper and wrapping paper. The density of the sheet before and after the shrinkingtreatment is shown below.

TABLE 11 Melting tempera- Density Density of Composition of unstretched sheet ture of of sheet the sheet the main after the after the Amount oiefinic primary secondary in parts resin stretching stretching Example No. Ingredients by weight C) (gJcmfi) (g./c.m.=)

135 Low pressure polyethylene 100 126 0. 727 0. 503

- Ethy ene/vinyl acetate copolymer-. Polybutadiene Po1ystyrene.. Silica powder Titanium oxide Zinc sulfide/barium sulfate mixture. 13G Medium low pressure polyethylene High pressure polyethylene resin Ethylene/vinyl acetate copolyrner Polystyrene Kaolin Diatomaceous earth.

EXAMPLE 137 Parts Polypropylene resin 110 Phenoxy resin Polybutadicne Diatomaceious earth 20 Silica powder 20 Titanium oxide 7 A composition of the foregoing ingredients (the melting temperature of the polypropylene resin being 174C.) was kneaded for 15 minutes by a kneading roll heated at 180C... and formed into a 0.5 mm thick sheet by a heat press. The sheet was cooled to room temperature, and then heated to 200C. Thereafter, the sheet was passed three times through rolls whose surfaces were maintained at 140C. immediately after passage, the sheet was stretched to 3 times its original length both in the longitudinal and transverse directions. Microscopic observation of the stretched sheet indicated that the surface layers have a porous structure, and the inner layer is voidless because of melting.

The stretched sheet was cooled to room temperature, and heated to 140C. The sheet was then stretched to 3 times its primarily stretched length at a rate of 50 Density of the Density of the Stretched sheet stretched sheet shrunk sheet of Example No. (g/cm") (g/cm) EXAMPLE 139 Stretched sheet of Example No. 1

Luster after treatment 29 Luster before treatment 29 30 33 33 i 3,, to v hmeltiaetens @WQQEEEPEEH?9 re and [02 25 35 B. further stretching uniaxially or multiaxially the re- 22 24 33 sulting stretched sheet at a temperature not higher than the melting temperature of said olefinic resin. 5 2. The process of claim 1, in which the further We claim: 1 A process f producing a synthetic paper which stretching step is carried out at a temperature of not comprises more than the melting temperature of said olefinic resin and lower than the temperature of the surface layers employed at the initial stretching. 3. The process of claim 1, in which said inorganic polymers and copolymers of C:l C4 wold-ins and filler is selected from the group consisting of diatomablends thereof, having a melt index of not more ceous earth, silica, talc, kaolin, zeolite, mica, asbestos, than and calcium carbonate, magnesium carbonate, calcium sulfate, clay, alumina, barium sulfate, zinc sulfate, lithopone, titanium oxide and zinc flower.

-4. The process of claim 1, in which the stretched sheet finally obtained is heat-treated at a temperature below the melting temperature of said olefinic resin under a tension which permits shrinking of the sheet. v 5. The process of claim 1, in which the stretched sheet finally obtained is callender rolled.

A. stretching multiaxially an unstretched sheet comprising a blend ofi 100 parts by weight of an olefin resin selected from the group consisting of homoii. 5 to 100 parts by weight of a thermoplastic resin having poor compatibility with said olefin resin and selected from the group consisting of styrene resins, polyacetal resins, polyacrylate resins, vinyl chloride resins, vinyl acetate resins and phenoxy resins; and

iii. 20 to 300 parts by weight of a finely powdered inorganic filler, while both surface layers are maintained at a temperature at least 10C. higher than The 9? of claim 1 wherem the.melt-mdex of the olefin resin IS 0.05 to 5.

that of the interior layer of the sheet but lower than 

1. AT A TEMPERATURE LOWER THAN THE MELTING TEMPERATURE OF SAID RESIN, THE TEMPERATURE OF THE INNER LAYER OF THE SHEET BEING DIFFERENT FROM THAT OF BOTH SURFACE LAYERS BY AT LEAST 10*C., AND
 2. AT A TEMPERATURE SUCH THAT EITHER ONE OF THE SURFACE LAYERS AND THE INNER LAYER IS MAINTAINED AT A TEMPERATURE LOWER THAN THE MELTING TEMPERATURE OF SAID RESIN, AND THE OTHER IS MAINTAINED AT A TEMPERATURE NOT LOWER THAN THE MELTING TEMPERATURE OF SAID RESIN AND HIGHER THAN THE MELTING TEMPERATURE BY 40*C. OR LESS. THE SYNTHETIC PAPER IS LIGHT IN WEIGHT AND HAS HIGH STRENGTH IN ADDITION TO OTHER DESIRABLE POROPERTIES AND FINDS UTILITY AS PACKAGING AND PRINTING.
 2. The process of claim 1, in which the further stretching step is carried out at a temperature of not more than the melting temperature of said olefinic resin and lower than the temperature of the surface layers employed at the initial stretching.
 3. The process of claim 1, in which said inorganic filler is selected from the group consisting of diatomaceous earth, silica, talc, kaolin, zeolite, mica, asbestos, calcium carbonate, magnesium carbonate, calcium sulfate, clay, alumina, barium sulfate, zinc sulfate, lithopone, titanium oxide and zinc flower.
 4. The process of claim 1, in which the stretched sheet finally obtained is heat-treated at a temperature below the melting temperature of said olefinic resin under a tension which permits shrinking of the sheet.
 5. The process of claim 1, in which the stretched sheet finally obtained is callender rolled.
 6. The process of claim 1 wherein the melt index of the olefin resin is 0.05 to
 5. 